The reliability of modelling and simulation of energy systems strongly depends on the prediction accuracy of each system component. This is the case of Stirling engine-based systems, where an accurate modelling of the engine performance is very important to understand the overall system behaviour. In this sense, many Stirling engine analyses with different approaches have been already developed. However, there is a lack of Stirling engine models suitable for the integration into overall system simulations. In this context, this paper aims to develop a rigorous Stirling engine model that could be easily integrated into combined heat and power schemes for the overall techno-economic analysis of these systems. The model developed considers a Stirling engine with adiabatic working spaces, isothermal heat exchangers, dead volumes, and imperfect regeneration. Additionally, it considers mechanical pumping losses due to friction, limited heat transfer and thermal losses on the heat exchangers. The predicted efficiency and power output were compared with the numerical model and the experimental work reported by the NASA Lewis Research Centre for the GPU-3 Stirling engine. This showed average absolute errors around ±4% for the brake power, and ±5% for the brake efficiency at different frequencies. However, the model also showed large errors (±15%) for these calculations at higher frequencies and low pressures. Additional results include the calculation of the cyclic expansion and compression work; the pressure drop and heat flow through the heat exchangers; the conductive, shuttle effect and regenerator thermal losses; the temperature and mass flow distribution along the system; and the power output and efficiency of the engine.

The Stirling engine is a closed-cycle regenerative system that presents good theoretical properties. These include a high thermodynamic efficiency, low emissions levels thanks to a controlled external heat source, and multi-fuel capability among others. However, the performance of actual prototypes largely differs from the mentioned theoretical potential. Actual engine prototypes present low electrical power outputs and high energy losses. These are mainly attributed to the complex interaction between the different components of the engine, and the challenging heat transfer and fluid dynamics requirements. Furthermore, the integration of the engine into decentralized energy systems such as the Combined Heat and Power systems (CHP) entails additional complications. These has increased the need for engineering tools that could assess design improvements, considering a broader range of parameters that would influence the engine performance when integrated within overall systems. Following this trend, the current work aimed to implement an analysis that could integrate the thermodynamics, and the thermal and mechanical interactions that influence the performance of kinematic Stirling engines. In particular for their use in Combined Heat and Power systems. The mentioned analysis was applied for the study of an engine prototype that presented very low experimental performance. The numerical methodology was selected for the identification of possible causes that limited the performance. This analysis is based on a second order Stirling engine model that was previously developed and validated. The simulation allowed to evaluate the effect that different design and operational parameters have on the engine performance, and consequently different performance curves were obtained. These curves allowed to identify ranges for the charged pressure, temperature ratio, heat exchangers dimensions, crank phase angle and crank mechanical effectiveness, where the engine performance was improved. In addition, the curves also permitted to recognise ranges were the design parameters could drastically reduce the brake power and efficiency. The results also showed that the design of the engine is affected by the conditions imposed by the CHP interactions, and that the engine could reach a brake power closer to 832 W with a corresponding brake efficiency of 26% when the adequate design parameters were considered. On the other hand, the performance could also be very low; as the reported in experimental tests, with brake power measurements ranging 52-120W.

This work presents the development and validation of a numerical model that represents the performance of a gamma Stirling engine prototype. The model follows a modular approach considering ideal adiabatic working spaces; limited internal and external heat transfer through the heat exchangers; and mechanical and thermal losses during the cycle. In addition, it includes the calculation of the mechanical efficiency taking into account the crank mechanism effectiveness and the forced work during the cycle. Consequently, the model aims to predict the work that can be effectively taken from the shaft. The model was compared with experimental data obtained in an experimental rig built for the engine prototype. The results showed an acceptable degree of accuracy when comparing with the experimental data, with errors ranging from +/- 1% to +/- 8% for the temperature in the heater side, less than +/- 1% error for the cooler temperatures, and +/- 1 to +/- 8% for the brake power calculations. Therefore, the model was probed adequate for study of the prototype performance. In addition, the results of the simulation reflected the limited performance obtained during the prototype experiments, and a first analysis of the results attributed this to the forced work during the cycle. The implemented model is the basis for a subsequent parametric analysis that will complement the results presented.

The use of simulation techniques for the study of Combined Heat and Power systems based on Stirling Engines (CHP-SE) has been focused on dynamic simulations that guide the sizing of the system components. These are valuable tools for the performance evaluation of determined designs. However, there is a need to complement these studies with additional analysis that could permit to assess the design improvement and the integration of the system components. For this reason, the present work developed a model that coupled the design equations of each component with the equations that describe the thermal interactions presented in the overall system.

This integration allowed to obtain a deeper insight into the thermodynamic characteristics of the overall system, and thus was used for the study of a micro CHP-SE experimental rig. The results for this case study allowed to quantify the main energy outputs, the energy losses, and the influence of different parameters on the system. The overall efficiency under the original conditions presented values ranging from 60%-64% with very low exergy efficiencies ranging from 5%-7%. The simulation analysis permitted to identify design and operational parameters that would increase the overall efficiency to values closer to 80% and the exergy to values closer to 14%. These increments would correspond to the reduction of the energy losses, improvements on the conditions for the biomass combustion, and the use of engines with higher electrical outputs.

5. Numerical simulation for the performance analysis of a gamma Stirling engine prototype

Computer assisted modelling and simulation of energy systems asses the performance and suggest improvements to achieve energy efficient solutions. This is the case of the Stirling engine technology, where computer simulations combined with experimental work have helped to the development of different prototypes. Following this trend, the current work aims to study possible improvements towards the design of a gamma Stirling engine prototype through numerical simulations. The prototype was first experimentally studied and presented low performances. For this reason and considering a lack of reports for this prototype, the numerical simulation was the approach to identify the possible problems that limited the performance. In this regard, this paper presents the development and validation of a numerical model that represent the performance of the Stirling prototype. The model follows a modular approach considering ideal adiabatic working spaces; limited internal and external heat transfer through the heat exchangers; and mechanical and thermal losses during the cycle. In addition, it includes the calculation of the mechanical efficiency taking into account the crank mechanism effectiveness and the forced work during the cycle. Consequently, the model aims to predict the work that can be effectively taken from the shaft. The model was compared with experimental data obtained in an experimental rig built for the engine prototype. The results showed an acceptable degree of accuracy when comparing with the experimental data, with errors ranging from 1%-8% for the temperature in the heater side, less than 1% error for the cooler temperatures, and 1-8% for the brake power calculations. Therefore, the model was probed adequate for study the prototype performance. In addition, the results of the simulation reflected the limited performance obtained during the prototype experiments, and a first analysis of the results attributed this to the forced work during the cycle. The implemented model is the basis for a subsequent parametric analysis that will complement the results presented.

The Dept. of Energy Technology at KTH, together with Universidad Autónoma de Bucaramanga, Colombia, studied the different possibilities for increasing the usage of palm oil residues for energy production in an optimized way. The main purpose was to maximize the use of the solid residues coming from palm oil extraction, substitute fossil fuels in cooking, reduce emissions and environmental impacts and improve the social/economic conditions of the region. The emphasis was in introducing the discarded solid residues – EFB - as a fuel and the effective use of fibres and shells. The study was based on several innovative and unique approaches that include the pelletization of EFB for gasification purposes, densification of fibres and shells for their use in different energy applications, anaerobic digestion of EFB for biogas production and a complete optimization of the energy system considering efficiency, technology availability, environmental issues and economic factors.

7. Collaboration of the Swedish-ukrainian universities in the development and implementation of the interactive multimedia teaching-learning system

The present report summarizes the experiences obtained in running the DSEE MasterProgram at the Department of Energy Technology, KTH, and in particular the performanceand results of distance students who started in autumn 2006 along the 1.5 year program.This is a review from the DSEE Program Coordinators’ side.

Solar energy is often available in abundant quantities in the vicinity of conventional steam power plants close to large energy-consumption centers, where also the need for clean add-on power is substantial. Fossil-fuel based power units (coal fired steam plants or natural gas fired combined cycles) can be augmented with solar thermal power for feedwater preheating or parallel steam generation. Especially relevant is if the solar field in such developments is designed to deliver lower temperatures when compared to solar-only steam units, therefore decreasing the costs for the solar hardware and its maintenance. Employing solar energy either for upgrade of existing large-scale utility plants or in new constructions avails also of their intrinsically high efficiency of energy conversion and established infrastructure. The potential benefits of solar-fossil hybrid steam cycles have already been widely recognized and various feasibility studies carried out. A more systematic approach for proper evaluation of efficiency gain is necessary, for several representative types and sizes of conventional utility steam plants. More straightforward optimization studies are also required for finding the optimum penetration of solar power in the fossil-fired steam cycle, taking into account both technological and economy values. The present work attempts to provide an exhaustive review of previous efforts in this field, summarize the potential for practical deployment, and primarily build up the basis for a normalized systematic approach upon which various broad optimization studies can be performed with the ultimate goal of examining the technical and economical feasibility of any solar-fossil integrated concept and ultimately proposing a viable practical application for any specific location.

This paper summarises the authors’ own teaching experiences from two large MSc-level courses taught as part of several international Master programmes related to Sustainable Energy Engineering, organized by the Department of Energy Technology at the Royal Institute of Technology (KTH) in Stockholm, Sweden.

Some important hinders and obstacles to effective learning are presented and discussed, addressing especially certain challenges for the students and their effect on student performance. Observations have been made throughout several years of increasing demand for energy- and sustainability-related knowledge by ever larger student groups. The growing number of international students and the fact that many students are aiming at expanding their abilities by specialising in energy engineering without having the necessary background, as well as the fact that many students following certain non-engineering programmes focusing on environmental or sustainability issues need nevertheless to study also purely engineering courses, brings many positive characteristics to the blended student team but also displays serious challenges to the practical optimisation of the learning activities, the intended learning outcomes, the speed of advancement in knowledge, and the general quality of education for such a diverse group of students.

Possible improvements and augmentations of the learning activities with the goal of finding solutions to these challenges on both a programme level and course level are proposed and subjected to testing in recent student batches. The expected results in terms of improved student performance, and the plausible further extension of this work, are introduced and analysed.

A desired feature of solar power systems would be to continue producing at high output a few hours after sunset in order to cover local peak loads. An energy storage system would be able to help with solving this problem. The simplest and most cost-effective energy storage method is a thermal accumulator, where hot water or another fluid is stored at a given temperature higher than the surroundings. Conversion of thermal energy into mechanical power when compared to photovoltaic systems, however, is limited in efficiency and requires comparatively complex equipment, which might not be as cost-effective as desired, suffer from low reliability and require frequent maintenance.

The thermal path of converting solar energy into electricity is certainly promising but has largely been underestimated and underutilized. Several thermal-to-electricity energy conversion technologies already exist in either conventional form or at close-to-commercialization phase and can be further optimized and adapted to low-cost low-temperature solutions. Combined heat and power (cogeneration) facilities at small scales can be attractive for a quicker and wider deployment in solar-rich locations.

This study evaluates and compares several candidates for the conversion of low-temperature solar thermal energy into power and examines their technical feasibility and thermodynamic performance, as well as their potential for low-investment strategies and integration with thermal energy storage. With temperatures in the solar collectors limited to 150

Results show that common steam, organic, or air expansion cycles optimized for low parameter applications are feasible for further development and deployment in the near future, based on established components featuring turbines derived from commercial products. Thermal-to-electricity efficiency of around 5% - 12% and solar-to-electricity efficiency of around 4 – 8% can be achieved by some of the cycle alternatives at their best operational conditions.

Agricultural residues continue to attract interest for energy recovery purposes as a renewable, CO2 neutral and increasingly cost-competitive alternative to traditional fossil fuels. Furthermore, some of these residues, like palm oil residues, represent a disposal problem for the processing industries, or they are not used efficiently. Several palm oil mills (POM) lack efficient energy systems and thus there is a considerable potential for improvement. These factors represent a strong driving force for the development of innovative polygeneration plants with combined electricity, heat and refined fuel production based on conversion of solid residues. This paper aims at analyzing the use of agro-industrial residues as fuel. For that, we propose different technology configurations based on the case of a small-scale palm oil mill in Colombia processing 30 tons of fresh fruit bunch per hour. The technology configurations include steam cycles using backpressure turbines, condensing-extraction turbines and also gasification-gas engine cycles in hybrid configurations. The possibilities to produce pellets from the residues from palm oil were also analyzed. The steam cycle base operational parameters were 20 bar and 350 °C. However, more advanced steam conditions (40 bar) were also considered and evaluated. All the analyses performed included a maximum of 60 % of the empty fruit bunch (EFB) produced in the POM for energy purposes due to its value as natural fertilizer in the palm oil plantations. The results show that the POM under study and other POMs that use electricity from the national grid have the capacity of being self-sufficient to cover of all their energy needs using the solid residues available. This means that POMs that currently only generate the required heat for the process can generate the electricity required and in some cases even an excess of energy that could be sold to other users with an adequate use of the residues available. Furthermore, based on the modeling done in Aspen Utilities Planner® it is shown that it is possible to cover the demand of the POM, the required energy demand for EFB preparation included possible pelletization of these residues and even generate an excess of electricity. In several of the configurations, excess electricity generation could be achieved in the range of 0.5–8 MW.

Since 1997 the Department of Energy Technology (EGI) has offered the Sustainable Energy Engineering (SEE) MSc Program to over 200 students from around 50 different countries. In June 2004, it was decided by the KTH President to offer the International Master Program on Sustainable Energy Engineering (SEE) as a distance program. Based on this, EGI offered a distance version of the Sustainable Energy Engineering Program (identified as DSEE) for the academic years (2004/2005 and 2005/2006) on a trial basis to a selected group of qualified students. This is a complete e-learning program that is held in conjunction with the regular SEE-program, offering an alternative for those students who could be accepted for the regular SEE-program but who can not afford to participate in the on-campus courses. All mandatory courses are offered on-line and lectures can be followed either synchronously or asynchronously via internet.This report contains the status of the first students that started the program in autumn 2004 and highlights the experience gained during the first year of the distance program as well as the challenges and opportunities associated with offereing a distance program in energy technology.

An overview of computerized educational program (CompEduHPT) which includes several simulations was presented. These simulations provide an alternative way to learn, based on discovery and experience. All the simulations were preceded with theory chapters, quizzes and preparatory tasks to enable fruitful exercises to be designed. Evaluations show that a computerized program including multiple ways of learning provides considerable support to the conventional student-teacher way of learning.

25. Gas turbine simulations in the computerized educational program CompEduHPT

An overview of the Computerized Educational Program (CompEduHPT) which includes different simulations was presented. These simulations give the students an outlook of the different parameters that affect the performance based on the ideal and real approach of gas turbine calculations. The simulations show the students the different aspects, effects and results when a calculation is made considering a mixture of two ideal gases. They also show the improvements in the performance of the gas turbine depending on the various options available.

26. Gas Turbine Simulations in the Computerized Educational Program CompEduHPT

Agricultural residues continue to attract interest for energy recovery purposes as a renewable, CO2 neutral and increasingly cost competitive alternative to traditional fossil fuels. The possibility of trigeneration in already established industries such as palm oil mills and coconut processing plants is very attractive especially when residues that otherwise represent a disposal problem can be utilized efficiently. Different technological scenarios for the production of electricity, process heat and biodiesel are analyzed using coconut and palm oil residues. Environmental aspects are also included in the analysis. Studies were conducted considering various scenarios to evaluate the feasibility of using these residues for energy purposes. The residues were considered to be combusted directly in steam boilers while steam turbines were used to generate electricity. Biodiesel is produced by transesterification of palm oil/coconut oil. The required process heat for palm oil or coconut oil processing as well as the steam required for biodiesel production is supplied by the combustion of the residues. The results show that palm oil mills/coconut processing industries can be independent of fossil fuels. Furthermore, they can contribute positively to the energy balance of the communities by helping reduce the dependence on fossil fuels and reducing simultaneously greenhouse gas emissions.

28. Optimal Upgrade of a District Heating Plant into a Polygeneration Plant Using Biomass as Feedstock

This paper aims at evaluating the possible upgrading of an existing district heating plant for production of electricity and pellets. The evaluation is carried out by optimizing the alternatives from the economic, thermodynamic and environmental point of view. In order to examine how the design can be optimized, a detailed model of the process has been elaborated using ASPEN Utilities and Matlab optimization toolbox. The parameters of the polygeneration plant have then been varied in order to examine how optimal economic benefit can be extracted from the biomass streams whilst still meeting the fundamental process demands of the industries and heat demand of the community. A multi-objective optimization has been used to investigate the Pareto-optimal trade-offs that exist between low electricity costs and investment cost. The resulting polygeneration plant designs conclude that it is feasible toproduce 18 and 25 MW of power while at the same time supplying the process steam required by the nearby industries and district heating for the community. The results also shown that it is feasible to operate the plant more hours per year by producing pellets and it could be possible to generate additional district heating (up to 25 ton/h of hot water) to cover the demands of a growing community.

Agricultural residues offer the possibility of reducing fossil fuel consumption, increasing energy security, and lowering greenhouse gas emissions. However, certain residues, like palm oil residues, either represent a disposal problem for the processing industries or they are not used and thus, there is a considerable potential for improvement. These factors represent a strong driving force for the development of innovative polygeneration plants based on solid residues. This paper considers an energy analysis of a Palm Oil Mill (POM) in Colombia processing 30 ton of Fresh Fruit Bunch per hour (FFB/h). Different heat and power generation options were considered with solid residues as feedstock. These configurations included steam cycles using backpressure or condensing-extraction turbines. The possibilities to produce pellets from the residues and biodiesel from palm oil were also analyzed. The steam cycle base operational parameters were 20 bar and 350 °C. More advanced steam conditions (40 bar) were also considered. The results show that it is possible to cover the demand of the POM and the required energy demand for residues preparation including possible pelletization and also biodiesel production. It is possible to obtain an excess of electricity between 0.4 and 3 MW if only residues are used.

Biomass-based fuels have attracted worldwide interest due to their plentiful supply and their environmentally friendly characteristics. In many cases they are still considered waste but for most industries in Sweden, biomass has changed from being simply a disposal problem to become an important part of the energy supply, thanks to the long-term efforts made by the government, researchers and industry, where energy policies have played an important role. However, the amount of power that could be generated from biomass resources is much greater than that which is currently used. To effectively capture this resource requires a new generation of biomass power plants and their effective integration into already existing industrial processes.The implementation of an integrated polygeneration scheme requires the simultaneous consideration of technical, economic and environmental factors to find optimum solutions. With this in mind, a unified modeling approach that takes into account thermodynamic as well as economic and environmental aspects was used. The analysis was done using ASPEN Utilitiesand the MATLAB optimization toolbox. A specific case of a sawmill in Sweden, with an annual capacity of 130’000 m3 of sawn wood, has been analyzed and different options for generating electricity and process heat (for the sawmill and fora district heating network) as well as densified biofuels was analyzed. Optimization was then applied for different configurations and operational parameters. The results show that the sawmill has the capability to not only supply its own energy needs, but also to export from 0.4 to 1MW of electricity to the grid, contribute 5 to 6 MWth of district heating and 20 000 ton/y of biomass pellets. The production of pellets helps to maintain the electricity production throughout the year when the district heating demand is lower. However, the levelized electricity cost is higher than the usual electricity price in the Nordic electricity market and may have difficulty to competing with low-cost electricity sources, such as nuclear energy and hydropower. Inspite of this, polygeneration remains attractive for covering the energy demands of the sawmill and pelletization plant.

The present report summarizes some experiences obtained in running the DSEE masterProgram at KTH.It gives the main experience, from the DSEE Program Coordinators side, of the student intakeduring the autumn 2005. It also illustrates some of the progress the students have made tilldate

Solar thermal energy and biomass fuels are often available at locations where they can benefit from combined hybrid energy utilization methods for the generation of electricity, representing suitable and advantageous integration alternatives. The feasibility of concentrating solar power (CSP) systems depends on cost limitations, desired installed power capacity and direct solar insolation, where smaller scales and low-cost solutions can often be preferred to large-scale investmentintensive installations. Biomass residues of various types, on the other hand, can be considered as proven fuels for small-to-midscale utility or industry based power or cogen arrangements and utilized through various technologies. The thermodynamic integration between a biomass fired power plant and a CSP unit can help to significantly increase the availability of the plant, improve its partial load characteristics, compensate for the intermittency of the solar energy resource while preserving the purely renewable profile of the generated electricity, and at the same time showing better overall performance when compared to two separate plants while avoiding the need for costly energy storage solutions. Biomass fuels can help reach better steam conditions in a steam plant based on CSP-generated steam, and thus improve the efficiency of energy conversion for the integrated hybrid system if compared with two individual single-fuel power units. In this study, an overview of feasible solar-biomass integration concepts is presented. A deeper thermoeconomic analysis of a selected integrated utility-scale biomass and CSP electricity generation plant is attempted, with certain simplifications. Furthermore, a multiobjective optimization strategy is regarded as very necessary and thus included in the analysis, where several major environmental aspects plus the cost of electricity are involved and defined in terms of desired parameters and conditions representative to Central Europe and Southeastern United States. The results are compared with conventional power generation alternatives. On that basis, a low-parameter CSP solution integrated with conventional biomass-fired combustion unit, where solar-generated steam is being superheated by the biomass fuel, has been chosen as the focus of the analysis in this study.

Biomass continues to attract much interest as a renewable, low-CO2, and increasingly cost competitive alternative to traditional fossil fuels for heat and/or electric power generation. At the same time, deregulation of electricity markets offer new opportunities for small-scale decentralized power plants (<20 MWe) in an area where traditional centralized technologies mostly dominate. These factors represent a strong driving force for the development of innovative small-scale combined heat and power (CHP) plants based on biofuels. This paper provides an overview of small-scale CHP with biomass as a fuel. A survey of existing plants in Sweden and Finland is presented, along with an overview of major energy conversion technologies under development. Information is provided related to energy taxation along with an outlook on future prospects.

District heating systems have contributed with the reduction of greenhouse gas emissions by also producing industrial steam, using waste heat from industrial process in the networks and integration of other industrial processes. This paper aims at evaluating the possible upgrading of an existing district heating plant for production of electricity and pellets. The evaluation is carried out by optimizing the alternatives from the economic, thermodynamic and environmental point of view. In order to examine how the design can be optimized, a detailed model of the process has been elaborated using ASPEN Utilities and Matlab optimization toolbox. The parameters of the polygeneration plant have then been varied in order to examine how optimal economic benefit can be extracted from the biomass streams whilst still meeting the fundamental process demands of the industries and heat demand of the community. A multi-objective optimization has been used to investigate the Pareto-optimal trade-offs that exist between low electricity costs and investment cost. The resulting polygeneration plant designs conclude that it is feasible to produce 18 and 25 MW of power while at the same time supplying the process steam required by the nearby industries and district heating for the community. The results also shown that it is feasible to operate the plant more hours per year by producing pellets and it could be possible to generate additional district heating (up to 25 ton/h of hot water) to cover the demands of a growing community.

36. On the optimal use of industrial-generated biomass residues for polygeneration

Increasing energy demand as well as climate change concerns call for an analysis and optimization of energy services. Efficient use of energy resources, mitigation of environmental effects and supply an increasing demand are just some of the issues that are relevant nowadays in the energy system. In this regard, worldwide efforts are being made to increase the use of renewable energy and to promote energy efficiency measures in order to reduce the emission of greenhouse gases.

Thus, sustainable solutions that take a holistic approach on covering the demands of the society are needed. The work presented herein addresses the use of industrial derived biomass residues for energy purposes in different contexts. The analysis was focused on: a) different alternatives to use solid palm oil residues in the Colombian mills for energy purposes including services b) the possibilities of implementing biomass-based heat and power plants in the Swedish energy system and their integration with already established biomass processing industries for polygeneration purposes.

The assessment of the palm oil residues consisted on a technical analysis of the possible alternatives for electricity, heat, and biofuels production. For that, a thermodynamic approach was used to evaluate different alternatives. The assessment of biomass power plant integrated with the Swedish industry considered the thermodynamic, economic and environmental factors associated with certain energy conversion technologies. In this case a multiobjective optimization methodology was used to perform the thermoeconomic analysis. This allowed the evaluation of two contrasting scenarios were polygeneration at industrial level could be suggested: a less economically developed country where environmental policies are limited and industrial energy efficiency has not been implemented and a high income country with energy and environmental policies well established and energy efficiency measures being encouraged.

Results show that the palm oil industry in Colombia has the capacity of being self-sufficient to cover of all their energy needs using the solid residues available. In the case of the thermoeconomic assessment of biomass-based integrated polygeneration plants in Sweden the results indicate that it is feasible to produce power while supplying the process steam required by nearby industries and district heating.

Agricultural residues continue to attract interest for energy recovery purposes as a renewable, CO2 neutral and increasingly cost competitive alternative to traditional fossil fuels. The possibility of trigeneration in already established industries such palm oil mills and coconut processing plants is very attractive especially when residues that otherwise represent a disposal problem can be utilized efficiently.

The use of these residues in rural areas or in small islands could certainly represent an advantage as the use of expensive fossil fuels represents an additional burden to foster development. Different technical scenarios for the production of electricity, process heat and biodiesel are analyzed using these residues Environmental aspects are also included in this analysis.

Studies were done considering certain scenarios to evaluate the feasibility of using these residues for energy purposes. Residues were considered to be combusted directly in boilers and steam turbines were used as prime movers to generate electricity. Biodiesel is produced by transesterification of palm oil/coconut oil. The required process heat for palm oil or coconut oil processing is supplied by the residues as well as the steam required for biodiesel production. The advantage is that biodiesel is a more flexible and easy-to-distribute fuel that can be used for power generation or for transportation. The results shown that palm oil mills/coconut processing industries can be independent of fossil fuels. Furthermore, they can contribute positively to the energy balance of the communities by helping reduce the dependence on fossil fuels and reducing at the same time greenhouse gas emissions.

Solar and biomass are indigenous renewable resources that can be used for electricity production and that together represent an interesting and suitable combination. Solar energy can be converted to electricity using photovoltaic (PV) panels or concentrating solar power (CSP) systems. The feasibility of PV and CSP for a particular location depends on the cost, desired installed power capacity and direct solar insolation. Biomass on the other hand, can be first gasified and thereafter converted to electricity. The use of biomass together with a solar plant can help to improve significantly the availability of the plant as it can compensate for the intermittency of the solar energy resource while keeping its renewable profile and at the same time avoid the need to install costly energy storage solutions. Furthermore, biomass can help to reach better steam conditions in a CSP plant and thus improve the efficiency of the system. This paper analyzes from the technoeconomic viewpoint an innovative 5MWe hybrid power plant that provides cost effective electricity using medium temperature Concentrated Solar Power (CSP) and biomass gasification technologies. The plant consists of parabolic troughs that provide saturated steam at 250oC; biomass gasification technology using a downdraft gasifier design with variable feedstock utilization capability; an innovative two stage boiler to produce superheated steam at 440oC at 40 bar; an Organic Rankine Cycle system to extract energy from the waste heat of the steam cycle and a membrane distillation unit to produce purified water. The result of this study shows that feedwater preheating and heating of the water up to saturated liquid conditions could represent an interesting option for a wider utilization of solar energy worldwide. In terms of cost, although higher than other alternatives, the installation of hybrid solar/biomass plants could still be attractive and could represent an important alternative in certain locations.

Small-scale biomass plants (< 20 MWe) represent a future possibility for an expansion of distributed generation using indigenous resources in Scandinavia. Today’s plants are typically operated in cogeneration mode but are characterized by low power-to-heat ratios and higher generation costs as compared to large-scale plants. However, the efficient use of biomass in a sustainable scheme requires the development of more efficient energy conversion systems. This paper explores possibilities to reach higher power-to-heat ratios and higher total efficiency levels with small-scale biomass plants producing electricity, district heat and/or district cooling (trigeneration). The analysis is based on flowsheet simulations of two modern cogeneration plants. Biomass pyrolysis and biomass gasification are combined with these base processes and the effect of the pyrolysed and gasified biomass amount to the power-to-heat ratios, electrical efficiencies and total efficiencies are simulated. Also district cooling production in trigeneration mode is studied as one promising option to increase the energy utilization of these processes. Advanced configurations for trigeneration are also discussed.